2002 Volume 51 Issue 10 Pages 929-935
It is well-known that the colors of azo compounds decrease with hydrogen peroxide, and that the reactions are accelerated in the presence of iron or manganese. Therefore, the phenomena can be used to determine iron and manganese by catalytic analysis. The discoloration of azo compounds with hydrogen peroxide has been explained by radicals produced as a result of the Fenton reaction. However, the hydroxyl radical and superoxide anion radical were presumed by only a UV-visible method in the presence of azo compounds. In this study, the radicals derived from hydrogen peroxide were confirmed by ESR in the presence of azo compounds. Hydroxyl radicals were detected by the ESR spintrapping method with 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). The amount of radicals obtained in the aqueous phase was estimated by the peak height in the ESR spectra. The typical DMPO-OH spectrum was obtained in the presence of an azo compound. The conditions were as follows: Fe, 0.33 ppb; H2O2, 0.4%; pH, 10.1; DMPO, 0.04 g; total volume, 1.5 ml; magnetic field, 337 ± 7.5 mT. Superoxide anion radicals were detected by using a reduction reaction of Nitro blue tetrazolium (NBT). Further, the anion radicals were confirmed by the suppression effect of superoxide dismutase (SOD) on the reduction reaction of NBT. The tridentate ligand azo compound has accelerated the Fenton reaction to work as an activator in the catalytic determination of manganese and iron. It was concluded that the radicals derived from hydrogen oxide attacked the azo compound to decrease the color of the azo dye as an indicator reagent.
